The present invention relates to PDP (plasma display panels) and more particularly to a method for implementing error diffusion on PDP so as to solve low level contouring occurred thereon.
The brightness of a typical color television (TV) may be expressed in following equation (1) in terms of input voltage by utilizing the physical characteristic of cathode ray tube (CRT) of color TV:
brightness=kxc3x97(VINPUT/VMAX)xcex3xe2x80x83xe2x80x83(1)
where xcex3=2.2, k is a variable representing gray scale of color TV (e.g., k=256 if gray scale of color TV is 256), VINPUT is input voltage varied as gray scale of color TV, and VMAX is a maximum voltage required for showing a maximum gray scale of color TV. Hence, the relationship of input gray scale versus output brightness of color TV may be plotted as a curve (FIG. 1a). Conventionally, prior to sending a video signal (e.g., NTSC or HDTV), a Gamma (xcex3) compensation process (called compensation process hereinafter) is performed on the original video signal by utilizing above physical characteristic thereof. That is, a compensation process is performed with respect to xcex3 in equation (1). As such, the relationship of input brightness versus output gray scale of color TV may be plotted as a curve (FIG. 1b). In one example of xcex3=0.45 (i.e., obtained from 1/2.2), the video signal received by color TV is converted into image for showing on screen of CRT of color TV. Hence, the relationship of input brightness versus output brightness of color TV may be plotted as a straight line (FIG. 1c). As a result, a high quality image is shown on the typical color TV without distortion.
As to recently available PDP (plasma display panels) brightness of respective discharge unit on panel thereof is controlled by discharge number. Hence, brightness may be expressed in following equation (2) in terms of discharge number as below (i.e., a straight line):
brightness=k2xc3x97discharge numberxe2x80x83xe2x80x83(2)
where k2 is a variable representing gray scale of PDP (e.g., k2=256 if gray scale of PDP is equal to 256). In view of this, the higher discharge number the brighter of PDP. This is similar to the effect that the larger input voltage the brighter of a typical color TV.
Referring to FIGS. 2a, 2b and 2c, a compensation process is performed on received video signal by PDP by substituting xcex3=0.45 into equation (1) by similarly utilizing the physical characteristic of typical color TV. As such, the relationship of input brightness versus output gray scale of PDP may be plotted as a curve (FIG. 2a). Further, the relationship of input gray scale versus output brightness of PDP may be plotted as a straight line (FIG. 2b). Furthermore, video signal received by PDP is converted into image for showing on screen of PDP. Hence, the relationship of input brightness versus output brightness of PDP may be plotted as a curve (FIG. 2c) by similarly substituting xcex3=0.45 into equation (1). As a result, a distorted image with poor contrast is shown on PDP.
Typically, an anti compensation process is performed for solving above drawbacks. In detail, in one example, an anti compensation process is performed on received video signal by PDP by substituting xcex3=2.2 into equation (1). As such, in PDP the relationship of input gray scale versus output gray scale may be plotted as a curve (FIG. 3b). In another example, an anti compensation process is performed on received video signal by PDP by substituting y=0.45 into equation (1). Hence, in PDP the relationship of input brightness versus output gray scale may be plotted as a curve (FIG. 3a). As to image shown on PDP, the relationship of input gray scale versus output brightness of PDP may be plotted as a straight line (FIG. 3c). By combining FIGS. 3a, 3b and 3c, in PDP the relationship of input brightness versus output brightness may be plotted as a straight line (FIG. 3d). In other words, a linear relationship exists between image shown on PDP and received video signal. As a result, a high quality image is shown on PDP without distortion.
As to current PDP, signal input/output and processing are done by a digital technique. Moreover, in most cases gray scale of PDP is expressed as a power of 2. For example, in PDP eight bits are needed for representing 256 gray scales. Typically, in performing a compensation process an analog-to-digital conversion is performed on video signal prior to substituting xcex3=0.45 into equation (1). Then an anti compensation process is performed by substituting xcex3=2.2 into equation (1) for effecting an inverse transform on video signal. Finally, an image is shown on PDP. As brightness of PDP is proportional to discharge number thereof. If brightness of one discharge of PDP is equal to N cd/m2 (N is an integer) N is a minimum brightness of PDP. As such, brightness of PDP may be expressed as a multiple of one discharge of PDP. That is, brightness of PDP is a multiple of N. Hence, brightness of a plurality of k discharges is k3xc3x97N (where k3 is a positive integer). In other words, a brightness of fxc3x97N is not obtainable if f is not an integer (e.g., a brightness of 0.5xc3x97N).
In view of above, it is known that a brightness of PDP can not be expressed by a discharge number having a non-integer value (e.g., decimal). Hence, the decimal has to be converted into an integer. In the case of the original video signal having 256 gray scales, the number of gray scale is reduced to 184 after first being processed in an analog-to-digital conversion and subsequently by substituting xcex3=2.2 into equation (1) for performing an anti compensation process thereafter. In another case that the original video signal having a gray scale of 22, the number of gray scale is reduced to 1.62738 after an inverse transform is performed by substituting xcex3=2.2 into equation (1). Since decimal fraction of gray scale can not be shown on PDP only gray scale having value one rather than 1.62738 is shown on PDP (see Table I below.)
Hence, a problem of insufficient gray scale of video signal is occurred in the range of low gray scale after such anti compensation process. And in turn a low level contouring is occurred in the range of low gray scale. Consequently, a poor contrast of gray scale is occurred in the range of low gray scale. This can degrade the image quality.
It is thus an object of the present invention to provide a method for implementing error diffusion on a plasma display panel (PDP) comprising the steps of: performing an anti compensation process on a received video signal of the PDP; diffusing an error generated by a first one of a plurality of pixels to a plurality of adjacent pixels; absorbing errors generated by the plurality of adjacent pixels by the first pixel; and multiplying each of a plurality of numeric weightings and the error of each of the adjacent pixels to obtain an error function of the first pixel. This utilizes a cost effective while simple addition circuit in implementing error diffusion for solving the problem of low level contouring in PDP due to insufficient gray scale of video signal in the range of low gray scale.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings.